Blade of a gas turbine

ABSTRACT

The blade has such a shape that the diameters of circles inscribing the belly and back sides at different positions of adjacent blades decreases as one goes from the front edge to the rear edge. Since the blade has such a shape, even if the influent angle and effluent angle of gases are increased, a deceleration passage is not formed in the passage between the adjacent moving blades.

FIELD OF THE INVENTION

[0001] The present invention relates to a blade, of a gas turbine,having a wide turning angle and suitable to a heavy duty and high loadgas turbine.

BACKGROUND OF THE INVENTION

[0002] General blades of a gas turbine will be explained by referring toFIG. 7 to FIG. 12. A gas turbine generally comprises plural stages ofstationary blades disposed annularly in a casing (blade ring orchamber), and plural stages of moving blades 1 disposed annularly in arotor (hub or base). Two adjacent moving blades 1 are shown in FIG. 7.

[0003] The moving blade 1 is composed, as shown in FIG. 7, of a frontedge 2, a rear edge 3, and a belly (or a belly side) 4 and a back (or aback side) 5 linking the front edge 2 and rear edge 3. Combustion gasesG1, G2, as shown in FIG. 7, flow in a passage 6 between the belly 4 andback 5 of two adjacent moving blades 1 at an influent angle α1 (G1), andturn and flow out at an effluent angle α2 (G2) By the flow of combustiongases G1, G2, the rotor rotates in a direction of blank arrow U throughthe moving blades 1.

[0004] The width of the passage 6 (“passage width”) of the moving blades1 in which the combustion gases G1, G2 flow gradually decreases from thefront edge 2 to the rear edge 3 as indicated by solid line curve in FIG.8. At the rear end 3, the width is minimum, that is, throat O. Thus, bynarrowing the passage width between the moving blades 1, along thedirection of flow of the combustion gases G1 and G2, the combustiongases G1 and G2 are expanded and accelerated, and the turbine efficiencyis enhanced.

[0005] Recently, in the field of gas turbine, the mainstream is the gasturbine of high load with the pressure ratio of 20 or more and theturbine inlet gas temperature of 1400 degree centigrade or more.

[0006] As the gas turbine of high load, the following two types areknown. One is a high load gas turbine in which there are a large number,for example, from four to five, of blades. The other is a high load gasturbine in which the work of each blade of each stage is increasedwithout increasing the number of stages of blades, for example,remaining at four stages. Of these two high load gas turbines, thelatter high load gas turbine is superior in the aspect of the costperformance.

[0007] To increase the work ΔH of each blade in each stage, it isrequired to increase the blade turning angle Δα as shown in FIG. 9 andFIG. 10, and equations (1) and (2).

ΔH=U×ΔVθ  (1)

ΔVθ=Vθ1+Vθ2  (2)

[0008] In equations (1) and (2), only the peripheral speed component Vθis defined in the absolute system, and the other peripheral speedcomponents are defined in the relative system.

[0009] More specifically, symbol U denotes the peripheral speed ofmoving blade 1. The peripheral speed U of moving blade 1 is almostconstant, being determined by the distance from the center of rotationof the rotor and the tip of the moving blade 1, and the rotating speedof the rotor and moving blade 1. Accordingly, to increase the work ΔH ofeach blade in each stage, it is first required to increase thedifference ΔVθ between the peripheral speed components near the inlet ofthe combustion gas G1 and outlet of the combustion gas G2.

[0010] To increase the difference ΔVθ between the peripheral speedcomponents, it is required to increase the peripheral speed componentVθ1 near the inlet of the combustion gas G1, and the peripheral speedcomponent Vθ2 near the outlet of the combustion gas G2.

[0011] When the peripheral speed component Vθ1 near the inlet of thecombustion gas G1 is increased, the influent angle α1 becomes larger.When the peripheral speed component Vθ2 near the outlet of thecombustion gas G2 is increased, the effluent angle α2 becomes larger.When the influent angle α1 and effluent angle α2 become larger, theturning angle Δα becomes larger (see FIG. 10). As a result, when theturning angle Δα is increased, the work AH of each blade in each stagebecomes larger.

[0012] Accordingly, as shown in FIG. 11 and FIG. 12, by setting theinfluent angle α3 and effluent angle α4 larger than the influent angleal and effluent angle α2 shown in FIG. 7, it may be considered toincrease the turning angle Δα1 larger than the turning angle Δα shown inFIG. 10.

[0013] However, the following problems occurs when only the influentangle α3 and effluent angle α4 are set larger. That is, the passagewidth becomes the passage width as indicated by single dot chain linecurve shown in FIG. 8.

[0014] As a result, as shown in FIG. 8, a maximum width 7 occurs at aposition behind the front edge 2, and a minimum width 8 occurs at aposition ahead of the rear edge 3, that is, a width smaller than throatO is formed. Therefore, as indicated by single dot chain line curve, adeceleration passage (diffuser passage) is formed from the front edge 2to the maximum width 7, and from the minimum width 8 to the rear edge 3.Accordingly, the flow of the combustion gases G1, G2 is decelerated, andthe turbine efficiency loss increases.

[0015] Thus, if only the blade turning angle is increased, the gasturbine with such blades is not suited to the heavy duty and high load.The problem is the same in the stationary blades as well as in themoving blades 1.

SUMMARY OF THE INVENTION

[0016] It is an object of the invention to present a blade, of a gasturbine, having a wide turning angle and suitable to a heavy duty andhigh load gas turbine.

[0017] The blade, according to the present invention, has such a shapethat the diameters of circles inscribing the belly and back sides atdifferent positions of adjacent blades decreases as one goes from thefront edge to the rear edge. Since the blade has such a shape, even ifthe influent angle and effluent angle of gases are increased, adeceleration passage is not formed in the passage between the adjacentmoving blades.

[0018] Other objects and features of this invention will become apparentfrom the following description with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is an explanatory diagram of influent angle, effluentangle, throat, rear edge wall thickness, and distance from coolingpassage to rear edge in the hub of moving blades in a first embodimentof blade according to the present invention;

[0020]FIG. 2 is an explanatory diagram of showing a passage of whichdiameter of inscribed circle of belly and back of adjacent bladesgradually decreases from front edge to rear edge of the same;

[0021]FIG. 3 is an explanatory diagram showing wall thickness, maximumwall thickness, blade chordal length, wedge angle, camber line, influentangle, and effluent angle of the same;

[0022]FIG. 4A is a graph showing characteristic of Tmax/C,

[0023]FIG. 4B is a graph showing characteristic of WA, and

[0024]FIG. 4C is a graph showing characteristic of d/O;

[0025]FIG. 5 is a graph showing the relation of turbine efficiency andturning angle in the blade of Gas turbines of the invention and theconventional blade of Gas turbines;

[0026]FIG. 6 is a graph showing the relation between the turbineefficiency loss and wedge angle;

[0027]FIG. 7 is an explanatory diagram of influent angle, effluentangle, and throat in the hub of moving blades showing the conventionalturbine blades;

[0028]FIG. 8 is a graph showing an ideal passage width and aninappropriate passage width;

[0029]FIG. 9 is an explanatory diagram showing direction of influentside combustion gas and direction of effluent side combustion gas;

[0030]FIG. 10 is an explanatory diagram showing the turning angle;

[0031]FIG. 11 is an explanatory diagram of a case with an increasedturning angle;

[0032]FIG. 12 is an explanatory diagram showing an increased turningangle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Embodiment of the blade of the gas turbine according to thisinvention will be explained by referring to FIG. 1 to FIG. 6. It must benoted, however, that the invention is not limited to this embodimentalone. In the drawings, same parts as in FIG. 7 to FIG. 12 areidentified with same reference numerals.

[0034] The blade of the embodiment, that is, the moving blade 10 islarge in the influent angle α3 and effluent angle α4, and also large inthe turning angle Δα1. For example, the effluent angle α4 is about 60 to70 degrees, and the turning angle Δα1 is about 115 to 150 degrees. Sincethe moving blade 10 has wider turning angle Δα1 (than the conventionalone), this blade is ideal and suited for the heavy duty and high loadgas turbine.

[0035] In the moving blade 10, as shown in FIG. 2, diameters R1, R2, R3,and R4 of inscribed circles 91, 92, 93, and 94 of the belly 4 and back 5of adjacent moving blades 10 are designed to be smaller from the frontedge 2 to the rear edge 3.

[0036] That is, the passage 6 is formed in the relation of diameter R1of solid line inscribed circle 91 (circle inscribing at front edge2)>diameter R2 of single-dot chain line inscribed circle 92>diameter R3of double-dot chain line inscribed circle 93>diameter R4 (throat O) ofbroken line inscribed circle 94 (circle inscribing at rear edge 3).

[0037] The moving blades 10 of the embodiment are thus composed, and ifthe influent angle α3 and effluent angle α4 are increased, decelerationpassage is not formed in the passage 6 between adjacent moving blades10. Therefore, the moving blades 10 of the embodiment present movingblades ideal for a gas turbine of large turning angle Δα1, heavy work,and high load.

[0038] A comparison of the efficiency of the conventional blades (movingblades 1) and the moving blades 10 of the embodiment will be undertakenby referring to FIG. 5. That is, in case of the conventional blade, asindicted in the shaded area enclosed by solid line curve in FIG. 5, whenthe turning angle Δα1 is more than about 115 degrees, the turbineefficiency drops suddenly. On the other hand, in the moving blades 10 ofthe embodiment, as indicated by broken line in FIG. 5, even if theturning angle Δα1 is more than about 115 degrees, a high turbineefficiency is maintained.

[0039]FIG. 3 is an explanatory diagram showing a specific configurationof the moving blade 10. In this blade, the turning angle Δα1 is about115 to 150 degrees. The ratio Tmax/C of maximum wall thickness Tmax ofmoving blade 10 and blade chordal length C is about 0.15 or more. Thewedge angle WA of the rear edge of the moving blade 10 is about 10degrees or less.

[0040] The manufacturing process (design process) of the moving blade 10is explained by referring to FIG. 3. First, the influent angle α3 andeffluent angle α4 are determined. Along the turning angle Δα1 determinedfrom the influent angle α3 and effluent angle α4, a camber line 9 isdetermined. Then the wedge angle WA of the rear edge is determined. Thewall thickness T and Tmax of the moving blade 10 are determined. As aresult, the moving blade 10 can be manufactured.

[0041] The ratio Tmax/C of maximum wall thickness Tmax of moving blade10 and blade chordal length C is about 0.15 or more in an area at thearrow direction side from straight line L in the characteristiccondition shown in the graph in FIG. 4A. The wedge angle WA of the rearedge of the moving blade 10 is about 10 degrees or less in an area atthe arrow direction side from straight line L in the characteristiccondition shown in the graph in FIG. 4B.

[0042] When these two characteristic conditions are satisfied, thepassage 6 indicated by solid line in FIG. 8 (as shown in FIG. 2, thepassage 6 gradually decreased in diameters R1, R2, R3, and R4 ofinscribed circles 91, 92, 93, and 94 of the belly 4 and back 5 ofadjacent moving blades 10 from the front edge 2 to the rear edge 3) isdetermined geometrically. That is, supposing the ratio Tmax/C of maximumwall thickness Tmax of moving blade 10 and blade chordal length C to beabout 0.15 or more, the portion of the maximum width 7 side indicated bysingle-dot chain line in FIG. 8 is corrected so as to be along the solidline curve as indicated by arrow. Supposing the wedge angle WA of therear edge of the moving blade 10 to be about 10 degrees or less, theportion of the minimum width 8 side indicated by single-dot chain linein FIG. 8 is corrected so as to be along the solid line curve asindicated by arrow. Thus, the design of the moving blade 10 is easy.

[0043] Further, as shown in FIG. 6, if the wedge angle WA of the rearedge of the moving blade 10 is more than about 10 degrees, the loss ofturbine efficiency is significant, but if it is smaller than about 10degrees, the loss of turbine efficiency is decreased. In FIG. 6, thebroken line shows the moving blade 10 with the effluent angle α4 of 60degrees, and the solid line shows the moving blade 10 with the effluentangle α4 of 70 degrees.

[0044] The moving blade 10 includes a cooling moving blade of whichcooling passage 11 is near the rear edge 3 as shown in FIG. 1. At therear edge 3 of the cooling moving blade 10, there is an ejection port 12for ejecting the cooling air (a). One or a plurality of ejection ports12 are provided from the hub side to the tip side of the rear edge 3 ofthe cooling moving blade 10.

[0045] The cooling moving blade 10 may be composed as shown in FIG. 1.That is, the ratio d/O of the wall thickness (d) of the rear edge 3 ofthe moving blade 10 and the throat O between the adjacent moving blades10 is about 0.15 or less.

[0046] The ratio d/O of the wall thickness (d) of the rear edge 3 of themoving blade 10 and the throat O between the adjacent moving blades 10is about 0.15 or less in an area at the arrow direction side from thestraight line L in the characteristic condition shown in the graph inFIG. 4C.

[0047] When the characteristic condition is satisfied, even in the caseof the cooling moving blade 10 of which cooling passage 11 is near therear edge 3, the passage 6 indicated by solid line in FIG. 8 (as shownin FIG. 2, the passage 6 gradually decreased in diameters R1, R2, R3,and R4 of inscribed circles 91, 92, 93, and 94 of the belly 4 and back 5of adjacent moving blades 10 from the front edge 2 to the rear edge 3)is determined geometrically. Thus, the design of the cooling movingblade 10 of which cooling passage 11 is near the rear edge 3 is easy.

[0048] Further, in the cooling moving blade 10 of which cooling passage11 is near the rear edge 3, as shown in FIG. 1, the ratio L1/d of thedistance L1 from the cooling passage 11 to the rear edge 3 (regardlessof presence or absence of rear edge blow-out; however, the length ofejection port 12 in the presence of rear edge blow-out) and the bladerear edge wall thickness (d) is 2 or less.

[0049] When the characteristic condition is satisfied, same as in caseof the blade (moving blade 10) set forth in claim 3 of the invention,even in the case of the cooling moving blade 10 of which cooling passage11 is near the rear edge 3, the passage 6 indicated by solid line inFIG. 8 (as shown in FIG. 2, the passage 6 gradually decreased indiameters R1, R2, R3, and R4 of inscribed circles 91, 92, 93, and 94 ofthe belly 4 and back 5 of adjacent moving blades 10 from the front edge2 to the rear edge 3) is determined geometrically. Thus, the design ofthe cooling moving blade 10 of which cooling passage 11 is near the rearedge 3 is easy.

[0050] An explanation if given above about the moving blades. However,this invention is applicable to stationary blades. By applying theinvention in the moving blades and stationary blades, the flow of thecombustion gases G1, G2 is smooth, and the turbine efficiency is furtherenhanced.

[0051] The conditions in the embodiment (the turning angle Δα1 of about115 to 150 degrees, the ratio Tmax/C of maximum wall thickness Tmax andblade chordal length C of about 0.15 or more, the wedge angle WA of therear edge of about 10 degrees or less, the effluent angle α4 of 60 to 70degrees, the ratio d/O of wall thickness (d) of rear edge 3 and throat Oof about 0.15 or less, and the ratio L1/d of the distance L1 from thecooling passage 11 to rear edge 3 and rear edge wall thickness (d) ofblade of 2 or less) may be satisfied at least in the hub portion of themoving blades 10.

[0052] As explained above, according to the blade of this invention,since the diameter of an inscribed circle of belly side and back side ofadjacent blades decreases gradually from the front edge to the rearedge, if the influent angle and effluent angle are set larger,deceleration passage is not formed in the passage between adjacentblades. Therefore, blade suited to a gas turbine of large turning angle,heavy work, and high load can be presented.

[0053] Moreover, the turning angle is 115 degrees or more, the ratio ofblade maximum wall thickness and blade chordal length is 0.15 or more,and the wedge angle of the rear edge is 10 degrees or less. As a result,the passage in which the diameter of an inscribed circle of belly sideand back side of adjacent blades decreases gradually from the front edgeto the rear edge is determined geometrically. Therefore, blade can bedesigned by an optimum design.

[0054] Furthermore, in the case of the cooling blade of which coolingpassage is near the rear edge, the ratio of wall thickness of rear edgeand throat between adjacent blades is 0.15 or less. As a result, even inthe case of the cooling blade of which cooling passage is near the rearedge, the passage in which the diameter of an inscribed circle of bellyside and back side of adjacent blades decreases gradually from the frontedge to the rear edge is determined geometrically. Therefore, it is easyto design the cooling blade of which cooling passage is near the rearedge.

[0055] Moreover, in the case of the cooling blade of which coolingpassage is near the rear edge, the ratio of the distance from thecooling passage to the rear edge and the wall thickness of rear edge ofthe blade is 2 or less. As a result, same as in the invention as setforth in claim 3, even in the case of the cooling blade of which coolingpassage is near the rear edge, the passage in which the diameter of aninscribed circle of belly side and back side of adjacent bladesdecreases gradually from the front edge to the rear edge is determinedgeometrically. Therefore, it is easy to design the cooling blade ofwhich cooling passage is near the rear edge.

[0056] Although the invention has been described with respect to aspecific embodiment for a complete and clear disclosure, the appendedclaims are not to be thus limited but are to be construed as embodyingall modifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

What is claimed is:
 1. A blade, of a gas turbine, having a wide turningangle, said blade having a belly side, a back side, a front edge, and arear edge, wherein diameter of circles inscribing the belly side and theback side of adjacent blades decrease gradually from the front edge tothe rear edge.
 2. The blade according to claim 1, wherein the turningangle is 115 degrees or more, a ratio of blade maximum wall thicknessand blade chordal length is 0.15 or more, and a wedge angle of the rearedge is 10 degrees or less.
 3. The blade according to claim 1, whereinthe blade is a cooling blade of which cooling passage is near the rearedge, and the ratio of wall thickness of rear edge and throat betweenadjacent blades is 0.15 or less.
 4. The blade according to claim 1,wherein said blade is a cooling blade of which cooling passage is nearthe rear edge, and the ratio of the distance from the cooling passage tothe rear edge and the wall thickness of rear edge of the blade is 2 orless.